Tarnish remover



I Patented Feb. 10, 1953 r Frederick A. Lowenheim, Plainfleld, N'- J.

No Drawing- Application December 21, 1949,

a claim. (oi. ass-4m 1 This invention relates to a comgsgiolriikfofigmmoving tarng' h and MM and e V e 1 1 meta 5 aces withoilr'iffackin themetal;

cleani such in silv silver p ate, 9 21:

, brass, bronze and other com r alloys.

its essence, the compositifidn'sistsessentially of an acid having a pK'in the range of 1 to 5 and thiourea. By the expression "p is meant thenegative logarithm of the dissociation constant, K. While not limitedthereto, it is intended to provide the composition in the form oi a drypowder mixture and to require a purchaser, before using the same, to addwater to the mixture, the amount of water to depend upon the characterof the impurities to be removed from the metal surfaces. T,he invention,however, also IIIH 8. com 0| 0:

The ingredients of the compositions are water-soluble.

Generally speaking, the dry mixture comprises a normally solid acidhaving a pK in the range of 1 to 5 and thiourea. Ihe amount otthioureashould exceed the amount of acid with the former comprising about 3 to 5parts 'by weight, 2

, in, or, as is preferable, by adding a wetting agent in solid form tothe dry powder mixture.

As examples of solid acids having a pK of 1 to 5, there may bementio'ned citric, o c, tartaric, phthalic, and succinic acids. as ister-insoluble c u l- I They are also a 0 ac cdspK oflessthan 1 are toocorrosive for the purpose intended, while acids having a pK greater than5 are inoperable. The preferred acids are the aliphatic. polybaslc.hydroxy acids like citric and tartaric, which are non-toxic andnon-irritating to the skin.

Besides thiourea, simple alkyl derivatives thereof such as methyl orethyl thiourea are also u sgf 1 i1 These derivatives are contemplated bythe expression "thiourea.

As wetting agents there may be mentioned such materia 1 alcoholderivatives, salts of substituted aromatic suliouicacids, sulfonatedfatty alcohols, sulfonated vegetable oil, highly sulfonated fatty acidesters, diglycol stearate, or-

ci wic do not form More particularly, It relates 55 a composition for" Mganic acid esters ofdiethylene glycol, N-alkylol fatty amides, w :aleneesters, complex amides of fatty ac g er a p a 10 and mixedaliphatic-aromatic quaternary ammonium hal- 5 ides, higher aliphaticamines, etc.

As an example of adry mixture, 200 parts of powdered thlourea and 50parts of powdered citric unaware mixed, and then 8 parts of a powderedcommercial l'auryl alcohol derivative was added thereto." This mixturewas dissolved in water, the amount of which is not critical, and wasfoundto be effective to remove the'tarnish from silver, copper andcopper alloys. Another powder mixture containing 50 g. of thiourea, 10g. of citric acid, and l g. of the above mentioned wetting agent wasadded to 1 liter of water. This solution was also found to be efiectiyefor removin tarnish from silver, co er and copper alloy articles merely5 di ping.

For impurities that are Hficult to remove, the action of the compositionmay be aided by incorporating an abrasive agent either to the drymixture or to the aqueous solution of the same and then employing aslight rubbing action in conjunction with the immersion treatment. Anyconventional abrasive such as infusorial earth, diatomaceous earth, etc.is useful for this purpose. As an example of a dry powder containing anabrasive, a mixture of 400 parts of thiourea, parts of citric acid, 10parts of wetting agent and 100 parts of diatomaceous earth was prepared.While desirable in some cases, an abrasive is not always necessary, asstubborn impurities can often be removed by treating them with anon-abrasive-containing composition to which just enough water has beenadded to moisten the powder without dissolving it. In such cases, onlyvery gentle rubbing may be necessary to efiect the desired result.

It may be noted that the dry mixtures disclosed herein possess adesirable advantage in being packageable in dry form, in distinction toa paste or liquid. The mixtures are not corrosive to ordinary packingmaterials, nor are the aqueous solutions of the same corrosive inrespect to the metals that are to be cleaned.

As indicated, other compositions comprising aqueous mixtures may beuseful. These prefer ably comprise acids that are normall li uid, suchas acetic formic, maleic and hgsphnric, all of which have a pK of 1 to5. Like the solid acids, they are water-soluble, stable, non-oxidizing,and do not form water-insoluble compounds with copper or silver.Compositions containing these acids may be formed as described above,

the thiourea going into solution. in the acid. Preferably a liquidwetting agent is used. As will be apparent, aqueous compositions forimmediate use may also be prepared from the solid acids.

In the light of the foregoing description, the iollowing is claimed:

1. A cleaning composition for silver-; and copper-containing metalsurfaces consisting 'essentially of 1 part by weight of an acid havingapKintherange oi 1to5 and about3 to 5partsby weight of thiourea, saidacid being watersoiuble, stable, non-oxidizing, and forming nowater-insoluble compounds with copper or'silver.

alloys comprising a dry powder mixture consist- 2. A cleaner for silver,copper, and copper alloys comprising a dry powder mixture consistingessentially of 1 part by weight of a solid acid having a mi in the rangeoi. 1 to 5 and'about 3 to 5 parts by weight of thiourea, said acid beingwater-soluble, stable, non-oiddizing, and forming no water-insolublecompounds with copper or silver, said mixture being adapted to bedissolved in water before use.

3. A cleaner for silver, copper, and copper alloys comprising a drypowder mixture consistin essentially of 1 part by weight of analiphatic, polybasic, solid acid having a pK in the range of 1 to 5 andabout 4 parts by weight of thiourea, said acid being water-soluble,stable, non-oxidizing, and forming no water-insoluble compounds withcooper or silver, said mixture being adapted to be at least partiallytreated with water before use.

"weight of an organic acid having a pK in the range of 1 to 5 and about3 to 5 parts by weight of thiourea, said acid being water-soluble,stable, non-oxidizing, and forming no water-insoluble compounds withcopper or silver.

8..A'.cleaner-for silver, copper, and copper -ing essentially oi'l'partby weight of a solid orgahic'acid having a pK in the range of 1 to 5 andabout 3 to 5 parts by weight of thiourea, said 4. A cleaner according toclaim 3 in which the acid being water-soluble, stable, non-oxidizing,and forming no water-insoluble compounds with copper or silver, saidmixture being adapted to be dissolved in water before use.

, FREDERICK A. LOWENHEIM.

Name Date 1,608,622 Schmidt et al Nov. 30, 1926 2,071,966 Bolton Feb.23, 1937 2,383,800. Johnson Aug. 28, 1945 2,393,866 Wassell Jan. 29,1946 2,485,529 Cardweil et al Oct. 18, 1949

1. A CLEANING COMPOSITION FOR SILVER- AND COPPER-CONTAINING METALSURFACES CONSISTING ESSENTIALLY OF 1 PART BY WEIGHT OF AN ACID HAVING APK IN THE RANGE OF 1 TO 5 AND ABOUT 3 TO 5 PARTS BY WEIGHT OF THIOUREA,SAID ACID BEING WATERSOLUBLE, STABLE, NON-OXIDIZING, AND FORMING NOWATER-INSOLUBLE COMPOUNDS WITH COPPER OR SILVER.